Gadolinia-doped Ceria Interlayer Research Articles

Unraveling the pivotal role of heterointerfaces on oxide ion transport in solid oxide fuel cells

Overcoming fundamental key issues affecting performance and stability has been recognized as the most important challenge for the commercialization of solid oxide fuel cells (SOFCs). Here, we employed a multipronged approach based on advanced nanoscale analyses coupled with electrochemical evaluation to elucidate the interrelation among ohmic resistance, oxide ion transport, and cation interdiffusion mainly occurring at the interlayer-electrolyte heterointerfaces. The presence of an interdiffusion layer (IDL), formed from the interdiffusion of Ce, Gd, and Zr during high-temperature sintering of conventional screen-printed gadolinia-doped ceria (GDC) interlayer on yttria-stabilized zirconia (YSZ) electrolyte, inadvertently acts as a major barrier to oxide ion transport and results in a significant increase of the ohmic resistance. An effective way to suppress the IDL formation and its oxide ion blocking effect is by alternatively fabricating the GDC interlayer using pulsed laser deposition (PLD), whereby dense layers prepared at a relatively lower deposition temperature without post-growth sintering can be obtained. Consequently, the cell's ohmic resistance is drastically lowered and a significant improvement in cell performance is achieved. These results have major implications for the selection and optimization of cell fabrication processes to mitigate degradation issues associated to heterointerfaces.

Investigation of the necessity to apply a (Ce, Gd)O2 interlayer between the low-temperature processed (La, Sr)CoO3 electrode film and the (Zr, Y)O2 electrolyte in solid oxide fuel cells

Gadolinia doped ceria (GDC) interlayers have been widely used to avoid resistive phase formation at the mixed ionic electronic conductor (MIEC) (La,Sr)CoO3 (LSC) air electrode/ yttria stabilized zirconia (YSZ) electrolyte interfaces. Although MIEC electrodes fabricated by low-temperature metal organic precursor methods offer the highest electrochemical performance, no studies exist on the effect of GDC interlayer on their performance. In this work, we investigated the necessity for a GDC interlayer between the low-temperature processed LSC electrode and the YSZ electrolyte. Through x-ray diffraction, scanning transmission electron microscopy/energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy analyses, we studied the impact of the GDC interlayer on i) the formation of resistive zirconate phases at the LSC/YSZ interface and ii) the overall phase and surface chemistry evolution. While no resistive zirconate phases formed in the LSC/YSZ system due to low processing temperatures, La leaching into the GDC layer altered the overall phase evolution, in addition to the resulting cation stoichiometry. This LSC/GDC/YSZ system showed a polarization resistance improved by an order of magnitude, attributable to the changes in phase composition.

Performance and stability analysis of SOFC containing thin and dense gadolinium-doped ceria interlayer sintered at low temperature

Gadolinium-doped ceria (GDC) interlayers are required to prevent the interfacial reaction between La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode and Y2O3-stabilized ZrO2 (YSZ) electrolyte in solid oxide fuel cells (SOFCs). However, it's difficult to prepare a thin and dense GDC interlayer on the sintered half-cell at a low temperature. In this study, the physical vapor deposition (PVD) method was employed to successfully manufacture dense GDC interlayers with the thickness of 1 μm. The influences of GDC sintering temperature (900 °C, 1000 °C and 1100 °C) on cell performance characteristics and degradation behavior were investigated. The cell with GDC interlayer sintered at 1100 °C showed the lowest degradation rate during the 216-h operation. The best stability was attributed to the most effective inhibition of Sr diffusion by the GDC interlayer, which was demonstrated by the almost unchanged Ohmic and polarization resistances during the aging stage and the negligible Sr enrichment at YSZ/GDC interface. Compared to the conventional screen-printed GDC interlayers (sintered above 1250 °C), the GDC interlayer prepared by the PVD method and sintered at 1100 °C was significantly denser and thinner, showing a promising application prospect due to its benefits for cell stability.

Performance Degradation in Proton-Conducting Ceramic Electrochemical Cells

Proton-conducting ceramics are a promising new class of electrochemical cells with a lower-temperature operational range in comparison to more-conventional solid-oxide or molten-carbonate counterparts. In the past, we have successfully demonstrated the scalability of this technology from the button-cell to the lab-scale stacks shown in the figure, along with strong performance and stability over thousands of hours under methane fuel at 550 ºC. This encouraging result was achieved through careful tuning of materials, fabrication procedures, and operating conditions. We have found that the degradation rates of protonic-ceramics stacks can be intense, especially at lower temperatures under fuel-cell operating mode. We have observed lower degradation rates under electrolysis operation, and at higher operating temperatures. These are both perhaps counterintuitive; lower-temperature operation is expected to improve the long-term stability, and degradation is typically more pronounced for more-common solid-oxide electrolyzers. In this presentation, we will review our studies on the root causes of performance degradation in protonic ceramics, and approaches to mitigate degradation.Previous work on performance degradation in oxygen-ion conducting electroceramics provides clues into the sources of degradation in protonic ceramics. That said, a number of degradation mechanisms are avoided by the nature of the protonic-ceramic device. For example, our microstructural characterizations reveal no nickel coarsening or agglomeration in the fuel electrode, likely due to the lower-temperature operation near 550 ºC. Operating conditions are shown to have a large impact on degradation rates in our protonic-ceramics; such conditions provide important clues about degradation’s root causes. Electrochemical Impedance Spectroscopy reveals how the slow kinetics of the electrochemical processes are closely tied to the degradation behaviors observed in our experiments.While we will continue to explore our root causes of degradation in proton-conducting electrochemical cells, we also report the impact of a gadolinium-doped ceria (GDC) interlayer on improving the durability of the cells, especially at low temperatures. This is perhaps a surprising, as GDC is a common O2--conducting material, and perhaps ill-matched to protonic ceramics. Regardless, the presence of the GDC layer at the air electrode - electrolyte interface has proven to be an effective strategy for minimizing protonic-ceramics degradation throughout our research, falling to 1.2% / 1000 hr for the methane-fueled stack at 600 ºC. While the root causes of this performance improvement remain unclear, we find the use of the GDC interlayer to impactful in reducing performance degradation in protonic ceramics. Figure 1

Lanthanum-doped ceria interlayer between electrolyte and cathode for solid oxide fuel cells

ABSTRACT Gadolinia-doped ceria (GDC) is widely used as an interlayer for preventing the formation of SrZrO3 between yttria-stabilized zirconia (YSZ) electrolyte and lanthanum strontium cobalt iron oxides (LSCF) cathode for solid oxide fuel cells (SOFCs). However, the diffusion of Gd ions to YSZ electrolyte results in the decrease in ionic conductivity due to the formation of Gd2(Zr, Ce)2O7. In the present work, we focus on lanthanum-doped ceria (LDC) as an interlayer between YSZ electrolyte and LSCF cathode. The ionic conductivity of YSZ/LDC composite was higher than that of YSZ/GDC composite in spite of the lower conductivity of LDC than GDC. The maximum power density for the microtubular SOFC with LDC interlayer was better than that with GDC interlayer. While the ohmic resistance decreased by the change from GDC to LDC interlayers, the polarization resistance for oxygen reduction reaction slightly increased as a result of distribution of relaxation times (DRT) analysis. The chemical compositions of Zr, Ce and La was gradually varied at the interface between YSZ electrolyte and LDC interlayer, which affected the both of ohmic and polarization resistances.

Surface analysis of lanthanum strontium cobalt oxides under cathodic polarization at high temperature through operando total-reflection X-ray absorption and X-ray fluorescence spectroscopy

The surface chemistry of perovskite-type lanthanum transition metal oxides is an important parameter in high-temperature electrochemical devices such as solid oxide fuel cells (SOFCs). Strontium segregation on the surface of lanthanum strontium cobalt oxides (LSC) may lead to poor oxygen reduction kinetics. However, previous studies have not sufficiently addressed the oxide surface chemistry, including the oxidation change of LSC under cathodic polarization. In this study, operando total-reflection X-ray fluorescence absorption and X-ray fluorescence spectroscopy were performed to investigate cathodic polarization at high temperature (773 K) and at 1 atm pressure. Dense thin-film electrodes of La0.6Sr0.4CoO3 (LSC113) on Zr0.92Y0.08O1.96 electrolytes with a gadolinium-doped ceria interlayer were examined as model SOFC cathodes. This may be the first time that predominant surface reduction of cobalt is directly observed by using LSC113 under cathodic polarization. This phenomenon is related to strontium enrichment on the LSC surface. (La0.5Sr0.5)2CoO4 decoration on LSC113 enhanced the oxygen reduction kinetics compared with that of bare LSC113. This is due to the suppression of cobalt surface reduction and Sr enrichment in the LSC113 phase.

Evolution of cathode-interlayer interfaces and its effect on long-term degradation

The degradation of electrochemical performance of solid oxide fuel cells (SOFCs) with long-term durability testing is generally evaluated in terms of increases in polarization resistances with time. Practical SOFCs normally employ an interlayer between cathode and electrolyte to improve the stability with long-term operation. To elucidate the relationship between the cathode-interlayer interfacial properties and degradation, various types of model interfaces based on La0.6Sr0.4CoO3-δ (LSC) thin film cathodes prepared on gadolinia-doped ceria (GDC) interlayers having different microstructures are investigated. Equivalent circuit analysis of the electrochemical impedance spectra reveals an increase of the interfacial resistance associated with degradation of the LSC/GDC interface with operation time. The physical origin of the interfacial resistance is attributed to the formation of yttrium-doped SrZrO3 (SZY) at the interface of LSC and GDC, a behavior which appears exacerbated for a nanocolumnar GDC interlayer. Investigation of model interfaces created with SZY inserted between LSC and GDC reveals large polarization resistances mostly dominated by the interfacial resistance, consistent with oxide ion blocking effects observed at interfaces. The role of the GDC interlayer microstructure on the long-term stability of LSC and GDC interfaces and cell performance is discussed.

A novel method to fabricate nanoporous gadolinium-doped ceria interlayer by combining wet-etching and thin film deposition

Fabrication of nanoporous doped ceria thin film by sputtering method has attracted attention for lowering operating temperature of solid oxide fuel cells and enhancing active sites for oxygen reduction reaction (ORR). However, it is difficult to obtain nanoporous structure of doped ceria by sputtering due to deposition characteristic of oxide thin film. A novel method for fabricating 300nm-thickness of nanoporous gadolinium-doped ceria (GDC) interlayer is developed by combining wet-chemical etching and co-sputtering. The nanostructure of thin film Ag-GDC cermet varied with deposition power of Ag and GDC was optimized for cathode interlayer. By etching Ag nanoparticle out of the Ag-GDC cermet interlayer, the highly porous nanostructure of GDC was obtained. The peak power density of the cell with nanoporous GDC interlayer was increased by more than a factor of 2.5 compared to that of the cell without the interlayer. Nanostructure and material properties of the GDC interlayer were analyzed by FESEM, XRD, and XPS.

In Situ Densification of Gadolinium-Doped Ceria Interlayer by Infiltration Process in SOFC

Gadolinium-doped ceria (GDC) interlayer is commonly inserted between electrolyte yttria-stabilized zirconia (YSZ) and cathode La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) to prevent the Sr migration from cathode to electrolyte and improve the stability of the solid oxide fuel cell (SOFC). However, it is difficult to make a dense GDC interlayer during the traditional process. Co, Gd and Ce nitrates solution is used as the infiltration solution to modify and in situ densify the GDC interlayer in this study. The GDC interlayer shows high density when it is pre-sintered at 1175°C and final sintered at 1300°C, and the cell shows high performance and stability, the voltage has little degradation after running for 100 hours at 800°C and 0.5Acm-2, Sr is not observed at the YSZ/GDC interface.

Effects of applied current density and thermal cycling on the degradation of a solid oxide fuel cell cathode

Effects of applied current density and thermal cycles on the durability of a solid oxide fuel cell (SOFC) cathode have been studied. SOFC half-cells with and without a gadolinium-doped ceria (GDC) interlayer were fabricated and tested for 1000 h at 900 °C under various current densities and thermal cycles. Performance degradation of the half-cells was assessed by increment of the area specific resistance (ASR). Initially, the ASR of the half-cells without the GDC interlayer decreased for around 150 h due to cathode activation and thereafter increased. A rapid increase in the ASR was observed at higher applied current density, which is attributed to delamination of the electrolyte/cathode interface due to the formation of Sr zirconates, and microstructural change in the cathode. However, these adverse effects were prevented by the GDC interlayer. The half-cells with the GDC interlayer exhibited a smaller degradation rate as compared to that without the GDC interlayer. During the thermal cycling test, ASR values of all GDC interlayer thickness cells increased with an increasing number of thermal cycles. The thermally cycled cell with a GDC interlayer thickness of 3.4 μm showed a lower degradation rate due to the dense GDC interlayer, which resulted in less interfacial resistance and prevented elemental diffusion towards the electrolyte. However, the half-cells with GDC interlayer thickness of 2.4 and 4.5 μm showed a higher increase in the ASR due to relatively higher Sr diffusion and delamination of the cathode/GDC interlayer interface, respectively.

Oxygen vacancy levels on gadolinia-doped ceria interlayer deposited by atmospheric pressure plasma jet for solid oxide fuel cells

The oxygen vacancy levels as a factor on different gadolinia-doped ceria interlayer (GDCi) films deposited on yttria stabilized zirconia (YSZ) electrolyte substrates by an atmospheric pressure plasma jet (APPJ) via precursor solution of nitrate salts are investigated. Focusing on the effect of carrier gases, scanning electron microscopy (SEM), Raman, and X-ray diffraction (XRD) are implemented for the materials characterization of the as-deposited GDCi films and sintered-GDCi films at various temperatures. The higher level of oxygen vacancies in GDCi films adhered on 8YSZ electrolyte are evidently analyzed using Ar as the carrier gas during the deposition, of which the interdiffusion resulted in the formation of (GDC + YSZ) solid solution for sintering over 1300 °C degraded the total conductivity. The deposition of GDCi films on 8YSZ by APPJ method using O2 carrier gas significantly improved the total conductivities of the whole electrolyte layers. Moreover, this study provides the useful insight into the oxygen vacancy levels on GDC films as interlayer (GDCi) to improve the values of open circuit voltage in LSM/GDCi/YSZ/Pt full-cell, as well as offering the efficiency of APPJ as one step deposition process.

In-situ Raman spectroscopy analysis of the interface between ceria-containing SOFC anode and stabilized zirconia electrolyte

The combined experimental approach for in-situ Raman spectroscopy of the inner “anode|electrolyte” interfaces in solid oxide fuel cells under current load was examined in a case study centered on the behavior of gadolinia-doped ceria (GDC) interlayers between cermet anodes and stabilized zirconia membrane. The Raman spectra of ceria at 850 °C were found sensitive enough with respect to the variations of anodic current and fuel gas mixture composition, which induce oxygen nonstoichiometry changes in GDC. Linear dependence of the Raman peak area on the open-circuit voltage makes it possible to estimate local overpotentials at the GDC interlayer|electrolyte interface under current load. The calculated local overpotentials exhibit a Tafel-like dependence on the current density, and are essentially independent on the hydrogen and water vapor partial pressures within the limits of experimental uncertainties. The relevant rate-determining mechanism may be associated with ion transfer via the GDC|zirconia interface, whilst the contributions of exchange-related processes involving gaseous phase are less significant in this interfacial zone.

Role of the gadolinia-doped ceria interlayer in high-performance intermediate-temperature solid oxide fuel cells

In this study, Ba0.5Sr0.5Co0.8Fe0.1Zn0.1O3-δ (BSCFZ) is used as a cathode with anode-supported scandia-stabilized zirconia (ScSZ) as the electrolyte to achieve intermediate-temperature solid oxide fuel cells (SOFCs). A gadolinia-doped ceria (GDC) interlayer is used between the BSCFZ cathode and the ScSZ electrolyte to protect ScSZ against interfacial reaction with the Co-containing cathode. However, an unfavorable reaction occurs at the GDC/ScSZ interface when the sintering temperature of the GDC interlayer is higher than 1200 °C. Thus, the performance of anode-supported SOFCs with GDC interlayers prepared at different sintering temperatures has been evaluated using I–V measurements and AC impedance spectroscopy. The results demonstrate that the sintering temperature of the GDC interlayer should be optimized for both the reaction between the BSCFZ cathode and ScSZ electrolyte and the reaction at the GDC/ScSZ interface. A maximum power density of 0.78 W cm−2 has been achieved at 700 °C with a GDC interlayer sintered at 1200 °C. Furthermore, the cell with the optimized GDC interlayer has been shown to maintain excellent reliability with respect to load cycling and thermal cycling.

Investigation of La0.6Sr0.4Co0.2Fe0.8O3- δ Electrode Performance and Microstructural Evolutions Based on Three Dimensional Microstructure Reconstruction and Electrochemical Simulation

The influence of initial microstructure of gadolinium-doped-ceria (GDC) interlayer on La0.6Sr0.4Co0.2Fe0.8O3- d (LSCF) performance was studied with three dimensional microstructure reconstruction by focused ion beam – scanning electron microscopy (FIB-SEM). When the GDC interlayer was fired at 1300 ˚C (GDC1300), discontinuous SrZrO3 phase was formed between GDC interlayer and yttria-stabilized-zirconia (YSZ) electrolyte. In addition, inter-diffused layer of GDC and YSZ was formed at the neighbor of the SrZrO3 phase and along the YSZ electrolyte interface. When the GDC interlayer was fired at 1200 ˚C (GDC1200), continuous SrZrO3 layer was formed. Inter-diffused layer was formed along the YSZ electrolyte. Both cells were operated at 700 ˚C and 800 ˚C . The initial electrode resistance of GDC1200 was more than 20 times larger than that of GDC1300. Slight increase of electrode resistance was found for GDC1300 after the cell operation, whereas the drastic activation was found for GDC1200. The activation was enhanced at operating temperature of 700 ˚C than 800 ˚C . For GDC1300, Sr rich phase was formed after the operation at 800 ˚C. It is considered that the differences of performance and microstructural evolution are highly dependent on initial microstructures and operating temperatures. The different electrode performances are evaluated based on electrochemical simulation using reconstructed microstructures.

Investigation of La0.6Sr0.4Co0.2Fe0.8O3- δ Electrode Performance and Microstructural Evolutions Based on Three Dimensional Microstructure Reconstruction and Electrochemical Simulation

The influence of initial microstructure of gadolinium-doped-ceria (GDC) interlayer on La0.6Sr0.4Co0.2Fe0.8O3- d (LSCF) performance evolution was studied. The cell with the GDC interlayer fired at 1300 ˚C (GDC1300), in which SrZrO3 phase shows discontinuous formation between GDC interlayer and yttria-stabilized-zirconia (YSZ) electrolyte, showed gradual increase of polarization resistance during 100 hours operation. In contrast, when the GDC interlayer was fired at 1200 ˚C (GDC1200), continuous SrZrO3 layer was formed between interlayer electrolyte interface, and the cell showed large polarization resistance with recovery during operation. The Strontium oxide phase was formed inside the LSCF cathode phase after the operation of GDC1300 at 800 ˚C, whereas the GDC1300 operated at 700 ˚C and GDC1200 operated at either 700 ˚C or 800 ˚C showed no decomposition of LSCF phase. It is considered that the differences of performance and microstructural evolution are highly dependent on initial microstructures and operating temperatures.

Influence of the electrode/electrolyte interface structure on the performance of Pr0.8Sr0.2Fe0.7Ni0.3O3-δ as Solid Oxide Fuel Cell cathode

The effect of gadolinium-doped ceria (GDC) interlayer on the Pr0.8Sr0.2Fe0.7Ni0.3O3-δ (PSFN8273) cathode performance and stability in solid oxide fuel cell (SOFC) operating conditions is investigated. Two different symmetrical half-cells, with dense GDC electrolyte pellet (GDC/PSFN cell) and with GDC interlayer deposited on yttria stabilized zirconia pellet (YSZ) (YSZ/GDC/PSFN cell), are prepared and characterized by electrochemical impedance spectroscopy (EIS) as a function of temperature. The fitting of the data is carried out using an adapted Equivalent Circuit (EC). The polarization resistance (Rp) is higher for the YSZ/GDC/PSFN cell compared to GDC/PSFN cell. This increase is assigned to the interface microstructure. Then, the electrochemical properties of the half-cell with GDC interlayer are measured in three-electrode configuration under dc cathodic overpotential. In addition, the long-term stability is evaluated through an ageing test applying a current density of −123mA.cm−2 for 1000hours at 700°C under air. PSFN8273 appears to be stable as cathode with a decrease in overpotential of about 6% in the first 200hours and a subsequently stabilization. These results mean that even if the GDC interlayer affect the cathode performance (in terms of Rp) it did not influence its stability, making PSFN8273 a suitable material as cathode for SOFC application.

Pore orientation of the gadolinia‐doped ceria cathode interlayer for a tubular SOFC using dip‐coating

AbstractAn active region of cathode interlayer in a tubular solid oxide fuel cell (SOFC) is structurally analyzed using a dual‐beam focused ion beam/scanning electron microscope (FIB/SEM). The GDC (10 mol% gadolinia‐doped ceria) cathode interlayer (about 1 μm in thickness) is dip‐coated, and then sintered on YSZ (8 mol% yttria‐stabilized zirconia) electrolyte. At 1150°C sintering temperature, the pores oriented more along the axial direction than the radial direction. The anisotropy of pore shape is accounted for the withdrawal force during the dip‐coating of the GDC interlayer.

Effect of SrZrO3 Formation at Lscf-Cathode/GDC-Interlayer Interfaces on the Electrochemical Properties of Solid Oxide Fuel Cells

Formation of oxide scales such as SrZrO3 (SZO) at the gadolinia-doped ceria (GDC)-interlayer/yttria-stabilized zirconia (YSZ) electrolyte interface during fabrication and operation negatively affects the electrochemical properties and long-term stability of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode/GDC/YSZ based solid oxide fuel cells (SOFCs). In this work, we investigated the effect of SZO formation at LSCF-cathode/GDC-interlayer interfaces on the electrochemical properties of LSCF/GDC/YSZ using scanning electron microscopy and electrochemical impedance spectroscopy. The GDC interlayers were grown on YSZ by pulsed laser deposition and fired using a multi-step heat treatment in air at 1400ºC for 1.5 h followed by 1000ºC for 10 h. The obtained GDC interlayer is dense with minimal cracks and pores avoiding the complexity arising from the porosity of the interlayer and cation diffusion via gas phase. The porous LSCF cathode layer with 12.0 µm-thickness was then screen-printed on top of GDC surface and fired at 1080ºC for 3.5 h in air. Cells consisting of LSCF cathode/GDC interlayer/YSZ electrolyte/Pt electrode was tested under open-circuit voltage and -0.3A cathodic polarization conditions at 800ºC for 300 h in air. It has been found that both cells showed an initial formation of nanosized SrZrO3 (SZO) particles along the LSCF/GDC due to the fast Zr transport in PLD-grown GDC interlayers after the tests. However, the size and distribution of SZO differ between the OCV and cathodically polarized interface. The SZO particles on the LSCF/GDC interface are substantially smaller and are highly distributed across the GDC surface in OCV as compared to cathodically polarized interface characterized by larger localized SZO grains. From this result, we infer that the SZO grains may have impaired the O2 reduction and oxidation reactions at the O2/LSCF/GDC triple-phase boundary (TPB) areas responsible for the observed increase in polarization resistances as a function of time. However, the formation and subsequent growth of larger localized SZO grains on the cathodically polarized LSCF/GDC interface may have led to oxygen permeable TPB areas corresponding to no apparent cell performance degradation. Our results show that the morphology, size, and distribution of SZO along the LSCF/GDC interface influenced the electrocatalytic activity of LSCF cathode affecting electrochemical cell performance.

Structure-designed gadolinia doped ceria interlayer for solid oxide fuel cell

A bi-structured gadolinia doped ceria (GDC) interlayer, which has a dense layer combining tightly with yttria-stabilized zirconia (YSZ) film and a porous layer with rough surface for contacting closely with the cathode, is prepared from a two-step sputtering process. Compared to the cell with a dense GDC interlayer, the single cell with the bi-structured GDC interlayer depicts greatly reduced ohmic and polarization resistances and increased electrochemical performance.

Proton-conducting Micro-solid Oxide Fuel Cells with Improved Cathode Reactions by a Nanoscale Thin Film Gadolinium-doped Ceria Interlayer.

An 8 nm-thick gadolinium-doped ceria (GDC) layer was inserted as a cathodic interlayer between the nanoscale proton-conducting yttrium-doped barium zirconate (BZY) electrolyte and the porous platinum cathode of a micro-solid oxide fuel cell (μ-SOFC), which has effectively improved the cathode reaction kinetics and rendered high cell power density. The addition of the GDC interlayer significantly reduced the cathodic activation loss and increased the peak power density of the μ-SOFC by 33% at 400 °C. The peak power density reached 445 mW/cm2 at 425 °C, which is the highest among the reported μ-SOFCs using proton-conducting electrolytes. The impressive performance was attributed to the mixed protonic and oxygen ionic conducting properties of the nano-granular GDC, and also to the high densities of grain boundaries and lattice defects in GDC interlayer that favored the oxygen incorporation and transportation during the oxygen reduction reaction (ORR) and the water evolution reaction at cathode.